1. Technical field
The present invention relates to a resinous unsaturated copolymer prepared by the random copolymerization of ethylene, propylene, or 4-methyl-1-pentene with a particular branched 1,4-diene.
It is well known that because of its excellent properties, a polymer consisting of ethylene or propylene only or a copolymer comprising ethylene or propylene and an .alpha.-olefin has been widely used in various fields.
However, these polymers are disadvantageous in that because they are saturated hydrocarbons, they are extremely inferior with respect to adherence, paintability and printability which are principally derived from a polar group. No fundamental solution to these problems has yet been found.
2. Prior art
A large number of inventions have been made on the copolymerization of an .alpha.-olefin and a non-conjugated diene. Among these, British Pat. No. 1,268,149, U.S. Patent Nos. 3,933,769 and 3,991,262 disclose inventions which are closely related to the present invention.
British Pat. No. 1,268,149 discloses an invention in which a finely divided colloidal titanium trichloride composition is used as a transition metal component of a polymerization catalyst, and the resulting copolymer is characterized by being in the form of a colloid having an average particle size of from 0.02 to 0.5 micron. All of the examples described in this prior patent relate to ternary copolymers comprised of two types of an .alpha.-olefin, particularly, ethylene and propylene, and one type of a non-conjugated diene. This prior patent disloses no example concerning binary copolymer comprised of propylene and a branched 1,4-diene or ternary copolymers comprised of propylene and two types of a branched 1,4-diene. This prior patent aims at producing a finely divided copolymer useful for a thin layer coating, and prepares a titanium trichloride catalyst component by reducing titanium tetrachloride with an organoaluminum compound in the presence of a small quantity of an .alpha.-olefin having at least 6 carbon atoms. However, the use of such a finely divided titanium trichloride catalyst component results in extremely finely divided unsaturated copolymer particles, which gives rise to an increase in the viscosity of the content of the polymerization vessel and difficulties in removing the heat of polymerization and in recovering the resulting unsaturated copolymer. Accordingly, the invention described in this prior patent cannot be readily carried out on an industrial scale.
U.S. Pat. Nos. 3,933,769 and 3,991,262 relate to the copolymerization of an .alpha.-olefin having from 4 to 12 carbon atoms and methyl-1,4-hexadiene, the resulting copolymer being characterized, by being rubbery.
As examples of copolymers comprised of ethylene and a diene, the following copolymers are known.
(1) Copolymers comprised of ethylene and a diene having a norbornene skeleton, e.g., ethylidenenorbornene (hereinafter referred to as ENB) (e.g. German Patent Laid-open Publication No. 2,001,702).
(2) Copolymers comprised of ethylene and a chain conjugated diene, e.g., butadiene (e.g., as disclosed in Japanese Patent Publication Nos. 16783/1974, 16784/1974 and 32270/1975).
These copolymers are disadvantageous in that because the control of the molecular weight is extremely difficult, the moldability is inferior (ethylene-ENB copolymers), and the activity during the polymerization process is remarkably low. Further, the resulting copolymers possess very poor thermal resistance and weather resistance because the copolymers have a C.dbd.C bond in the main chain, or the tertiary carbon atom of the main chain is present in an allyl position (ethylene-butadiene copolymers). Accordingly, all of these copolymers are not suitable for practical use.
Considering the thermal resistance and weather resistance of the copolymer from the standpoint of molecular structure, it is preferable that the C.dbd.C bond be attached to the main chain of the copolymer as a pendent group, and, at the same time, the tertiary carbon atom of the main chain form no allyl position. As an example of a comonomer providing such a copolymer, mention may be made of 1,4-diene. However, 1,4-hexadiene, which is representative of such 1,4-dienes, not only reduces the polymerization activity of a polymerization catalyst, but, its use also results in a copolymer whose molecular weight is greatly varied when the amount of hydrogen added during the polymerization is changed by even a slight amount. Accordingly, the use of this 1,4-diene is not suitable for the industrial production of copolymers.
As a technique for producing unsaturated copolymers by copolymerizing .alpha.-olefins and polyenes in the presence of a Zeigler-Natta catalyst, there is a well known technique for industrially producing a so-called EPDM, which is an elastomer, by copolymerizing ethylene, propylene and a non-conjugated diene in the presence of a Ziegler-Natta catalyst by using a vanadium compound as a transition metal component. Various non-conjugated dienes may be used in the production of the EPDM. Examples of such non-conjugated dienes are dienes having a cyclic structure such as norbornadiene, dicyclopentadiene, propenylnorbornene, methylenenorbornene and ethylidenenorbornene and linear dienes such as 1,4-hexadiene, 1,5-octadiene, 1,6-decadiene and 1,9-octadecadiene.
A Ziegler-Natta catalyst using a vanadium compound as a transition metal component is a representative catalyst for the production of the EPDM. However, the catalyst of this type is disadvantageous in that because the resulting copolymer is easily colored even if a minor quantity of vanadium is remaining in the copolymer, a complicated process in which the remaining catalyst is thoroughly removed from the copolymer after the polymerization is completed is absolutely necessary, that the resulting copolymer does not possess high stereospecificity, and that the polymerization activity is remarkably reduced with the elapse of time.
On the other hand, when a Ziegler-Natta catalyst using a titanium compound as a transition metal component, which is a typical catalyst for the production of crystalline and resinous polyolefins and can be advantageously used on an industrial scale, is used for the copolymerization of .alpha.-olefins and the above-mentioned polyenes, other problems are encountered, although the above described disadvantages experienced in the case of the vanadium type catalyst are eliminated. That is, the control of the molecular weight of the resulting copolymer with hydrogen is greatly hindered by the action of the polyenes present, or even with a very slight change in the quantity of hydrogen added, the molecular weight of the resulting copolymer is greatly varied, which makes the molecular weight control on a practical scale remarkably difficult. Another possible result is that the polymerization activity is remarkably reduced, or the stereospecific property of the resulting copolymer is remarkably reduced.
For example, when a high stereospecific catalyst comprised of (a) a solid catalyst component having, as essential ingredients, magnesium chloride, titanium tetrachloride and ethyl benzoate, (b) triethylaluminum and (c) ethyl p-toluylate is used for the copolymerization of cis-1,4-hexadiene and propylene, only 4% by volume of cis-1,4-hexadiene, based on the concentration of the charge, which corresponds to a cis-1,4-hexadiene unit content of 1.6 mole % in the resulting copolymer, reduces the catalytic activity to one-tenth of that in the case of the polymerization of propylene only, and the boiling n-heptane insoluble matter (hereinafter referred to as I.I.) of the resulting copolymer is only 65% (Reference is made to Comparative Example C1). In the case where the copolymerization of ethylidenenorbonene and ethylene is carried out in the presence of a catalyst comprised of a solid catalyst component having, as essential ingredients, magnesium chloride, ethoxy titanium trichloride, and triethylaluminum, the control of the molecular weight of the resulting copolymer by hydrogen is completely impossible (see, Comparative Example C2), and the resulting copolymer is very difficult to shape.
It is known that the presence of hydrogen in an .alpha.-olefin polymerization system including a Ziegler-Natta catalyst reduces the molecular weight of the resulting copolymer. It appears that the behavior of hydrogen as a molecular weight controlling agent is particularly conspicuous in the production of crystalline and resinous polyolefins. It is considered that, provided that an appropriate amount of hydrogen is used, hydrogen has an influence on only the molecular weight of the resulting polymer but has no significant influence on the other properties of the polymer such as stereospecificity, the composition of comonomers in the case of copolymerization and the polymerization activity of a catalyst.
However, as stated above, hydrogen does not behave advantageously in a copolymerization system in which non-conjugated dienes co-exist over a catalyst whose transition metal component is a titanium compound, and, accordingly, a titanium type catalyst is much inferior in practical value for the above-mentioned copolymerization system.